Signaling system



Feb. 13,1940- G. s. VERNAM rs1-A1. 2,190,301

` SIGNALING SYSTEM Filed July 10, 1935 4 Sheets-Sheet 1 @mig Feb. 13', 1940.

G. S. VERNAM El' AL SIGNALING SYSTEM Mii BOX

ha 50x55 INVENTOFLS' W 5. vm BMJ. WHW

v AzORNEIY Feb. 13, 1940. G. s. VERNAM r-:r A1. 2,190,301

l S'IGNALING SYSTEM Filed July 10, 1935 4 Sheets-Sheet 3 7 8 9 4 72157-62 mcfrc.

Feb. 13, 1940. G, VERNAM Er AL 2,190,301

.SIGNALING SYSTEM Filed July 10, 1935 4 Sheets-Sheet 4 zaf- fa/MTM BY M M :Ell

Patented Feb. 13, 1940 Unirse STATE-.s

SIGNALIN G SYSTEM Gilbert S. vernam, Hackensack, N. J., and Ronald S. Wishart, Rockville Centre, N. Y., assi'gnors vto Postal Telegraph-Cable Company (New York), New York, N. Y., a. corporation of New York Application July 10, 1935, Serial No. 30,630

7 Claims.

This: invention relates to new and useful improvements in signaling systems, and more particularly to cali circuit registering and testing arrangements.

The main object of the present invention is to provide a switching arrangement at a central oice. whereby, il faults develop on call circuits terminating at the office, the nature of' the fault maybe determined andthe continued operation of the system insured by the simple expedient of sequentially operating a switching device through plurality of predetermined positions.

The switching device may, in accordance with one embodiment of the invention, consist of two keys. By operatingr one key or the other, or both keys` together, the circuits at the office may be readjustedl to compensate for all abnormal loop` conditions.

In accordance with another embodiment of the invention, a rotary switch is providedv at the oilice. The switch is moved step by step from oney position to another to provide the required rearrangement ci the circuits should a fault develop on a loop.

Another object of the invention is to provide a* switching arrangement for associating testingr equipment with any one o1" a plurality of loop circuits. The switching may be performed byv the' alternatel actuation of contacts provided on two keys, or vby means of a rotary switch which successively connects the testing equipment with any one of the' conductors of a plurality of loops. connected with thev oice.

These and other` objects of the invention will more fully appear from the following detailed description oi embodiments thereof' and the appended claims;

In the drawings, Figs. lv and 2 represent diagrammatically signaling. systems' which the switching is controlled, respectively, by means off keys, andI by means of rotary switches;

l, 3 and 3o are, respectively, a plan view and a vertical cross-section ofv a rotary switch;

Fig. (i is ythe circuit diagram of a main; oilice which may be connected with the system shown in Fig. 2;

diagraminatically illustrates a inodication of the test equipment switching device iliustratcd in Fig. 2; and

6; and' 7` are, respectiveiy, iront and side elevations of an assembiy of the switching devices diagrammatically indicated in Fig. 2.

Referring to Fig. l., a pluralityv of call boxes ia and; lb are associated with the incoming conductor l, and a plurality oi' call boxes 2 and 2b are associated with the outgoing line 2 of a line circuit loop. Fifty or more boxes may be connected in series with a loo and there is no distinction between the boxes until a fault occurs whiel'iyin eieot, divides the loop into two separate lines, some of the cal-l boxes being in the' outgoing and the others in the incoming side of the fault. Conductor i is connected through normally closed? contacts 91 and 4 of key T, the Winding of relay A, Contact fl oi key O, and contact 2 of key G to ground. The iine 2`v is connected over conta-cts B and 3' of key T, the winding of relay B, and a resistance 3 to grounded battery. As Well known, each call box has twov code wheels (see box Ib), one for grounding the line and the other for opening it. The line isiirst grounded and then interrupted for each signal impulse transmitted. Normally, the line circuit loop is ciosed over the various call boxes and both relays A and B are energized and maintain their armature attracted. When the line is grounded relay A becomes deenergized and it will remain deenergizeilkv when the line is opened. Relay B remains energized when the liner is grounded at a call box, but becomes deenergized when the line is opened.

Upon its deenergization, relay A `closes a circuit i'rom ground, through the windings of register and bell magnets 5 and 6 in. series, and a signal lamp 'lf in parallel, the armature and back Contact of. relay A, contact 2 of key O, and resistance i3 to grounded battery, operating the register, the bell and the signal lampin the'usual manner. Similarly, when relay B becomesdeenergized, it closes a circuit from grounded batte-ry 4', through resistance B', contact 2' oi"v key O, the back contact and armature of relay B, and Contact 3 of key O, to operate magnets 5 andr 6 and the lamp 'l'.

During normal operating conditions, the register 5, the bell G and lamp T are intermittently operated audibly and visually toindicate and record' the designation of the box from which a call is sent. Should the line become permanently grounded or open, one or both of the relays A and B would release, permanently lighting lamp i and ringing bell 6. To determine the nature ci the trouble, the attendant rst actuates ground key G and leaves the open key O` in its normal position. If the lamp 'l still remains lighted, the key O also actuated. Ii the lamp remains lighted, key G is restored to normal and key O left actuated.

In response to one of these operations, the lamp 'i3 becomes extinguished and the condition of thel keys G and O indicates the nature of the line trouble; (l) when lamp 'I is out with both keys normal, the line is normal; (2) with key G operated and O normal, the lamp goes out if the line is grounded; (3) with G normal and O operated, the lamp goes out if the line is open; and (fi) with both keys actuated, ir" one orthe other side of the line is grounded, and the other open, the lamp goes out.

The circuits in case (l) have already been traced. In case (2), relay B is held energized by the permanent ground on the loop, since its winding is connected direct to grounded. battery over resistance 3. Relay A is energized over key contacts O4 and G1. Interruptions of either loop conductor will be repeated by Vone of the relays.

In case (3), both relays become deenergized upon the opening ci the line, but with key G normal and O actuated, the lamp circuit is interrupted in contacts Il and 3 of key O. Ground impulses applied to either conductor of the loop will operate one of the relays and the call will be recorded in the usual manner.

In case (4), the lamp circuit will be prepared through the armatures and fro-nt or back contacts of relays A and B, contacts G5 and OI, and resistance 8 to grounded battery. This circuit will, of course, be closed only when one of the relays is operated from a call box.

The operation of either key or both keys will, in contacts GI and 2 and O4 and 5, switch relay A from ground to grounded battery, whereby under all line conditions register 5 can be controlled from a call box.

In case (4), since grounded battery is connected through resistance 8, key contacts OI and G5 to the armature of relay B, open circuit impulses from call boxes on the grounded line section will release the relay that happens to be energized, connecting register 5 to the battery over the back contacts of relays A and B in series. Ground impulses from boxes on the open side of the loop will operate B or A (whichever happens to be released) to close the register circuit through the front contacts of the'two relays in series.

It will be seen, therefore, that the register will operate regardless of the side of the loop which 'is open or grounded and it is not necessary lto have separate switch settings for the grounded and open and the open and grounded conditions as is the case with usual call circuit arrangements. y

When it is desired to switch line I, 2 to another oiiice (e. g., for night service), the right- .hand contacts of key T are actuated and the line extended overcontacts l and I Il. By actuating the left-hand contacts of key T, the loop is connected with a test circuit common to a plurality of call circuits I and 2, I, 2', etc. Only one key T, T', etc., should be moved into the testing position at a time.

In the test circuit, the line I extended thro-ugh contacts T5 is connected to contacts L@ and 'I and through T6 and relay A to the normalground connection, and line 2 over TI to L2 and 3 and through T2 and the normal circuit to battery 4. If now the left-hand contacts of lkey L are operated,a circuit is closed from grounded battery 4, through relay B, I'I L4, BE and 3, milliammeter 9, call box Ill, B'I and 2, LI, T2 and B, to conductor 2 and including milliammeter 9 and call box III in the line. The milliammeter 9 indicates the current in the outgoing line 2 and the call box I0 can be used to send signals over this linein a manner similar to the normal call box operation By operating the right-hand contacts of key L, a similar test may be made of the incoming line I through the circuit traced above.

When key B isy operated in either direction, a tone test relay II and a buzzer I2 are substituted in the last traced circuit for meter 9 and box Ill by opening contacts B2 and B3 and including relay II in series in the line through BI and B4 when B is operated to the left, and by opening contacts B'I and B8 and including relay I I in series in the line through B6 and B9 when B is operated to the right. The lefthand contacts of key B, when closed connect thefbuzzer I2 through the armature and front contact of relay I I, and B5 to grounded battery. Under the control of relay II, the buzzer I2 operates to locate open faults. When the righthand contacts are operated, the buzzer circuit extends through the back contact of relay II and BIIl for locating grounds. The lineman tests for open faults by means of a telephone receiver I3 which by means of a clip I Il and a needle point I5 he connects from the line to ground, depressing button I6 to shortcircuit a condenser I1 thus completing a closed circuit through relay I I when the point grounded is on the side of the line away from battery 4. This will operate relay II which, in turn, operates buzzer l2, the tone generated being coupled to the line through condenser It. If the point grounded is on the other side of the open fault the circuit will not be completed through II and accordingly no tone will be generated. The tone Y its circuit completed through the grounded point of the line, it will normally be energized. Releasing key I will open the line, releasing relay II and closing the circuit through the buzzer I2, producing a tone in receiver I3. If the test is made on the side of the grounded point in the line remote from the tone tester, no sound will be heard in the receiver I3.

In the arrangement shown in Fig. 2,. a single rotary line switch 5I! having five positions is substituted for keys G and O and the right-hand l contacts 'I-IIJ of key T of Fig. l. A rotary test switch 5I, common to a group of not more than live loops, is operable to connect the testing equipment to either side of any loop, thus replacing the left-hand contacts I -5 of key 'I' and contacts I-- of key L of the arrangement shown in Fig. 1. v

The switches 5B andk 5I consist each of 'three sections, one of which is shown in Figs. 3. and 3a. These sections are mounted on a common shaft 52. Each section has two rotating segments or rotors 53 and 54 of conducting material. The rotor sections are so shaped as to surround shaft 52 but are spaced therefrom. They are held `together and mounted on the shaft by means of a disc 55 of insulating material to which the rotor segments are riveted. The disc 55 has a crossshaped perforation which ts over a section of screW and bushing are shown broken ori to inrconstitute a six-pole ive-position switch.

segments 53, 54 has a projection 5ll=t and 58", respectively, Which operate as Wipers and are diagrammatically represented in Fig. The Wipers cooperate with a circular bank o1' te minals, i-,5 for each Wiper, mounted on a ring of insulating material surrounding shaft 52. A common contact ttamounted on ring *il engages the rotorsection and a common Contact 515a also mounted on ring 'all rotor segment 54 in all positions of shaft 52. Each section is,

therefore, a twopole five-position switch, and

three such sections mounted on av common shaft Only five of the six poles are used in the line switch Sii. Ring 5'! is fastened by means of tubular bushings 58'1'nounted on screw threaded rods 58@ to a plate 59. The vhead of screw is above plate 59 and the screw extends through lower plate 5l into another tubular bushing. Both dicate that additional contact plates may be added as required. Actually the switch has three plates like 5l and a bottom bearing plate for shaft 52.. Corrugations @il formed in plate A5,9

are engaged by a ball (il carried by the free end of. a leaf spring The other end of spring di is doubled hack as indicated p` orated to t over section 6d. of shaft cil. Section 5d is shaped like section 515 and, when shaft 52 is rotated by means of a mounted in front of a panel S5, it carries with it spring corrugations Stare so positioned th and b will be properly centered on a terminal when ball El rests in a recess between two corrugations Sil. Suitablestops (not shown) are provided to prevent spring @il C id, therefore, the shaft and rotors from rotating vbeyond the No. 1 or No. 5 positions.

,The handle 55 of the line, switch [nl is normal ly in the position marked normal on l (Fig. 6), but when line trouble occurs, indicated by a steady light of signal lamp-8??, it is rotated one step at a time to the right until the lamp goes out. The circuit will then receive calls in spite of the trouble and the pointer of 'switch 'knob 65 indicates the natureof the trouble. The

extreme right position of the switch is used for transferring the loop to another office for Service.

liti-C resistance 85 to `the bach contacts of relays A1 and B1. relay B1 is Open at Elib, but the armature of relay A1 is connected. With the signal lamp re t? and a 10W resistance relay the latter controlling buzzer 89. Relay A1 will release in response to each impulse from any call box and will cause will permanently release its. armature and will cause continuous operation of lamp register magnet lll and buzzer Gil. attendant will nofw rotate the knob of the line switch shaft. En the. second or ground position, 'the rlp 56 is extinguished and the buzzer stops because both relays A1 and B1 become energized, ground being supplied from the line loop, and battery being supplied to A .through resistance 90 and wiper e, and to B1 through resistance 82. The winding of B1 is now connected With the outgoing line through the #2 terminal of 5011. Since over 50 battery applied only to the back contacts of A1 and B1, the register circuit Will be open. Relay A1 will respond to impulses from call boxes on the outgoing and relay B1 to impulses from. the boxes on the incoming side of the ground fault, whereby calls from any box Will be properly registered.

Should the loop go open, relay B1 remains deenergised, relay A1 becomes deenergized, and

lights steadily. When switch 50 is rotated into the second position the lamp remains lighted over a circuit including resistance 86, 55.310, the back contact and armature. of relay .A1 .in parallel over 50C, back contact and armature of B1 and 56h. The attendant now rotates the switch into the #3 or open position, whereby battery 84 is transferred through resistance and C fromI the back to the front contacts of relays A1 and. B1. The lamp becomes extinguished and relays A1 and B1 may beL operatedA by ground impulses from call boxes on their respective sides of` the loop, A1 being supplied with battery through 50,11 and B1 through 82.

If the loop goes open and one` side becomes grounded, relay A1 becomes deenergized as before. When switch 50 is rotated into the second and third positions, one of the relaysA1 orkB1 will operate and the other remains released, de pending on Which side of the line is open and which side grounded. The circuit of lamp Will be closed through the, back contact of one of these relays While the switch is in the second position, and through the front contact of the other relay while the switch is in the third position.. When, however, thek switch is rotated intothe fourth position, battery is applied through 03 and 58C to the armature of relay B1 Which..is disconnected from the register circuit infthe open #el terminalof 591. The relay contacts are new connected to operate. inseries as in Fig. l when both'keys G and O are operated. rEhe lamp is extinguished and ground impulses from call boxes inthe open side ofthe loop will operate one relay, closing the register circuit through the front contacts of lboth relays in series. Open impulses from boxes in the grounded side of the loop will release the other relay and close the register circuit through the back contacts of both relays in series, so that calls from any box will bey properly recorded.

In the lfth position of switch 5E?, loop 8i, 85 is connected through 50d and e, and conductors tl, 92. to another orfthe main oflice. Both relays A1 and B1 become deenergized and, since battery is connected to. their back contacts through 56C, lamp 80 will light. This is a warn., ing signal that power switch 83` be opened or that switch be returned to normal. The last mentioned indication isv useful when the power si is closed upon the beginning of. the next business day.

It the same kind of call circuit equipmentv is used at the main oilice to which `the loop is transferred night service, the arrangement at this oilicc is shown in Fig. el. This circuit is the saine branch oilice circuit (Fig. 2.) except for changes in the Wiring of the fifth contacts associated with rotors |0011, d and e of switch idd, corresponding to switch 50. At the main oihce, switch Hill is left in the fifth or transfer 'position during the dayr while the circuit is in use at the branch oice. When the branch office switch is turned to the transfer position, the loop is` closed through conductors 9| and 92 to the main oflice and relay A11 operates, lightingthe signal lamp 801. The main oi'ce attendant should then rotate the switch |v to its normal position, where it will operate `during the night period. In case of line trouble, the main cnice equipment will function as described for the branch office. When the branch oiiice opens in the morning and restores its line switch to normal to take over `the messengerservice', relay A11 at the main oice will release'and light the lamp 901 as inthe case of an open line. The main oice switch |00 should be rotated then to the transfer position, restoring the circuit to its regularday- Y time condition.

Referring again to Fig. 2, the test switch 5| and its associated equipment are common to two call circuit loops. In its normal or No. 1 position, loop 8|, 85 extends through wipers 5|a and 5|b and loop Sla, 82a extends through wipers 5Ic and Fig. 1.

5|d, and the testing equipment is disconnected.`

When rotated to its No. 2 position, switch 5| opens the outgoingline 8| and connects test call box 93 and jack 94 in series with this line. The test call box may now be used to check the operation of the relays vA1, B1 and ymillarnmeter 95 may be plugged into the test jackk 94 to measure the outgoing line current as described in connection with Fig. 1. The relay may be tested by transmitting signals in the usual manner and properly manipulating the switches at the call station. The test jack 94 may also beused by the lineman for connecting a portable tone test set 95 to the line to aid in locating line trouble in a manner fully set forth in connection with The functioning of the tone test equipment was also' described in connection withv Fig.`1.

Switch y5|, when rotated to the third position, closes the outgoing line 8| and connects the testing equipment in series withthe incoming line 85. This switch when rotated to positions 4 and 5, connects thetesting equipment in a similar manner in series with either side of the second call circuit loop Bla, 82a.

Although switch 5|, asshown in Fig. 2, is used for testing only four line conductors (or two loops), it lis obvious that it could be expanded to handle more circuits by adding rotors yand switch contacts. By usinga single rotor, formed as a ring with one projecting wiper (see |5|f and g of Fig. 5), each section of the switch becomes a single-pole |-position switch. With 12 such sections, l0 wired like 5|ad to 5|d, and two wired like 5|@ and 5|f, the switch could be used to test 10 line conductors or both sides of ve call circuitA loops. l

The same result can be accomplished, however, by using only sevensections |5|2-, arranged and wired as shown in Fig. 5, except that the sections are placed along a common shaft instead of being arranged side by side as shown.`

The first ve sections, |5|ae, of switch |50 each have four rotor pieces oi special shape and each section is arranged to close two line circuits independently, opening each one of these in only one position of the shaft. `For example, it can be seen that circuit #l is normally closed through contacts of the rst switch section |5|a, but will be opened i1` the switch is rotated one step clockwise as the two short terminal springs |52 and |53 will both be opposite short portions of the" rotor. For any other position of the rotor the circuit will be closedv because the long center contact spring |753 will be connected to either one or the other of the two short springs |52, |53 through a rotor segment. The same rotor will open circuit 5 when the shaft is rotated six steps form its normal position. The contact springs for the second section |5|b are placed one step (30) around in a clockwise .direction as compared with the rst section |5|e, so that circuits v2 and 'I will` be opened, respectively, when the" The by the other ve sections.

This test switch |5| will connect the testing circuit |55v in series with any one of ten line conductors, or either sidewof any oneof iive call` circuit loop circuits, and is, therefore, equivalentto the usual type of vcord and plug and ten line jacks. It is also considerably cheaper than the customary cord and vjackarrangement, is more compact and has a better appearance. Where there are more than five loops, a second similar test switch can be connected to the upper right-- hand terminals |56. The rst test switch must be placed in its normal position to extend `the testing circuit to the second switch. `A third switch can be connected to the second in a smilar manner.

`Figs. 6 and 7 show the assembly of a call circuit vswitchboard for two loop circuits, and illustrate the unit typeconstruction used with the rotary switch type of equipment. The two line units are shown in the upper part of Fig. 6. Each consists. i

of a bent steel bracket 200 held at the bottom by screws 20|a threaded into posts 20| whichf'frv support the resistance 91." Attached to bracket 200 are the line switch with extended shaft 52, socket 202 for lamp 05, kpanel 66, terminal strip 203, and insulating block 204 on which are mounted the two relays A, B. ,One end of the bracket is held by a' turned-over portion ofthe shelf 201|a and the'other end is fastened 'by a screw 205 to a block205 attached to the same shelf. By removing a single screw 205, the unit can be removed from theshelf 204e.

to which are attached two brackets 208 which support the shelf `2014, a terminal strip 209 and a front panel 210. sistances 82, 86, y is mounted on the base 201 and the call box 93, test switch 5|, power switch 83 and `binding posts ,2H are mounted on the front panel2l0. A test jack 94, as shown in Fig. 2 may be usedy instead of these binding posts.

The assembly is enclosed withina casing 2|2;

'Ihe assembly of a larger' switchboard for a larger number of loops will kbe arranged rin the same manner as the two-line switchboard. If

the board is not completely equipped for, say ten A lines, blank panels can be substituted for some of the line units.

The .lower part cf. the switchboard consists of a base 20'!v In this case the test switches,

A resistance unit .2I0 (re-f. H (i0 one for each ve loops, preferably of the type l shown in Fig. 5, are mounted as separate umts in a manner similar to the line units. As in the smaller switchboard, the lower part includes the battei'ytap resistances, line terminal 'strip and testing equipment. It should be noted that panel 66 is held to bracket 20B by a single screw, so thatv by attaching switch handle 65 and then removing this screw, the front ofthe relay is accessible vfor 'cleaning `contacts or adjusting. The terminals 2'l3 on strip ima 'are 'also accessible 'for testing. By removing screw 2135 and the ten wires from these terminals, the entire lineunits `may be pulled out from the iront, with this arrangement, the entire equipment is accessible for niaintenance purposes veven though a large number of Vthe units are installed in a case mounted against a wall. Standard telephone relay racks may also be used for mounting this equipment in units or shelves of five line relay units one test switch. v

We claim: v

'1. A signaling system, comprising a line loop having a first and second terminal, a plurality of call boxes each comprising a signal transmitting device for intermittently interrupting the loop and connecting it to ground connected in said loop, a central 'oiiice at which said loop is terminated and a source of current at said'oiiice having one terminal grounded and the other terv minal normally connected to said first loop terminal, said other loop terminal being normally grounded, characterized by means for rendering said system operative during abnormaiconditions of said line, such as grounding, open circuit or a `combination of both conditions, comprising a rst and second relay at said office, switch means at said ofce. having a normal and only three other control positions, each of said three other control positions representing a different one of said abnormal conditions on said loop,acircuit for said first relay from ground to said second terminal of the loop closed in the normal position and from said source to said second terminal ot said loop closed in the three other positions of said 4switch means, a circuit said second relay from said other terminal of said source of current directly over said irst loop terminal, separately closed only in said three other yposit-ions of said switch means, whereby said second relay is connected with they loop for eiecting signal control only in said three other positions but not in the normal position of said switch means, said rst relay being operatively .connected with said loop for response to signals in normal and three other positions oi said switch means, front contacts for said relays connected 'together and back contacts for said relays connected together, relay varmature contact means controlled by said first and secon-d relays, a call register, and circuit connections including said contacts and armature contact means adjusted by said switch means for controlling said register by said first relay only in the normal position of said switch means, and independently by either oi relays in said three other positions of said switch means.

2. A signaling system according to claim. 1 wherein said switch means comprises two key controlled switches for establishing said normay and abnormal circuit operation conditions.

3. A signaling system according to claim 1 wherein said switch means comprises a plurality of uni-controlled multi-position rotary switches ci' substantially similar form for establishing said normal and abnormal system operation conditions.

1. A signaling system, comprising a line loop having a first and second terminal, a plurality of call boxes each comprising a signal transniitting device for interrupting the loop and connecting it to ground connected in lsaid loop, a central oflice at which said loop is terminated and a `source of current 'at said cnice having one terminal vgrounded and the other terminal Vnormally connected to said first loop terminal, characterized by means ior rendering said 'system operative during abnormal vconditions ol said line,

` such as Agrounding open rcircuit or a combinationI ol both conditions, comprising 'a first and second relay at said office each having front vand back 'l contacts, switch means at said `oilicef having ar normal and 'only three othercontrol positions,

each of vsaid three other control positions repre-` senting a `diieren-t one of said abnormal condi#A tions on said loop, 'a circuit for said rst relay from ground to said second terminal of the loop 'closed in the normal position and from said source to said second terminal of said loop closed in the three other positions of said switch means, a cir-A cuit f'or said second relay from said otherterminal of said source of current directly over said first loop terminal, separately closed only in said three other positions of said switch means, whereby said second relay is connected with the loop for Aeffec-ting signal control only in said three other positions `but 'not in the normal position ci said switch means, `said first relay being operatively connected with said loop i'or signal vcontrol in the normal and three other positions oiz said switch means, means connecting togetherv tire front contacts and the back contacts of said relay-s, relay armature contact means controlled by said rst and second relays, a call register,

circuit connections including said rst relay contact and 'armature for controlling said register by oper-ation `of said iirst relay contacts only, in the normal position of said switch means, and

other circuit connections including said armatures and contact means of both said relays aol-"40 justed by said switch 'means for controlling said l register independently by either oi said relays in said 'three other positions of said switch means. 5. A signalingsystem, comprising a line loop having a first and second terminal, a plurality line, such as grounding, open circuit or a com-- binati'on of both conditions, comprising a first and second relay at said cnice, switch means at said 'oiiic'e having a normal and only three other control positions, each ol said three other control positions representing a diiierent one of said abnormal conditions on said loopa circuit for said rlrst relay from ground to said second terminal of the loop closed in the normal position and from said source to said second terminal of said loop closed in the three other positions oi' said switch means, a circuit i'or said second relay from said source of current to said iirst loop terminal separately closed only in said three other positions of said switch means, whereby said second relay is connected with the loop for effecting signal control only in Said three other positions but not in the normal position of said switch means, said rst relay being operatively connected with said loop for response to signals in the nom-zal and three other positions of said switch means, iront contacts for said relays connected together and back contacts for said relays connected together, relay armature contact "means controlled by said rst and second relays,

a callregister, a signal means normally conv trolled by said iirst relay only, and actuated upon occurrence any of said abnormal conditions iny said loop connected in parallel with said register,

circuits including said contacts and armatures controlled by said relays for releasing said signal .ineansupon operation of said switch means to a position corresponding to the abnormal condition of said loop, and -circuit connections including `said armatures and contacts controlled -by said switch means for controlling said register, by said rst relay vonly in the normal position of said Vswitch means, and independently by either of minal grounded and the other terminal'normally connected to said rst loop terminal, characterized by means for rendering said system operative during the abnormal conditions of said line,

' such as grounding, open circuit or a combination `of both conditions, comprising a first and second'relay atsaid oflice, a multi-position rotary switch at the oflice having a normal and three other positions, each intermediate position representing a diiTerent abnormal condition on the loop, a circuit for said i'lrst relay from ground to said second terminal of the loop closed in the ,norrnal position of said switch and from said source 'to said second terminal closed in the three other positions of said switch, a circuit for said second relay from said source to said rst loop terminal closed only in the three other positions of said switch, said first terminal being connected to said source in all positions of the switch,

whereby the second relay is operatively connected rwith said `loop only in said other but not said normal position of the switch and the iirst relay is operatively connected with the loop in the normal and the other positions of the switch, front contacts for said relays connected together and back contacts for said relays connected together, relay armature contacts controlled by said rst and said second relays, a register controlled solely by said iirst relay contacts in said normal position of the switch and by either of said relay contacts in said other positions of said switch,

` a signal connected in parallel with said register normally controlled solely by the rst relay and actuated upon the occurrence of an abnormal condition on either limb of said loop, circuits 'including said contacts and armaturescontrolled by said relays for releasing said signal when the switch is set into anintermediate position'cor- A 5 responding to the abnormal condition of the loop, and connections including said contacts and armatures for controlling said register by either 4'of said relays in said other positions of said v acterized by means for rendering said system op-2 erative during abnormal conditions of said line, such as grounding, open circuit or a combination of both conditions, comprising a rst and f second relay at said oflice, a rst switching key anda second switching key, each key having ahz rst and second switch position, normal switching position comprising said two keys in their first position, and positions for abnormal conditions cf said loop comprising either one or both oi said keys in said second position dependent, 3

upon the nature of said condition, a circuit for said first relay from ground to said'second terminal of the loop closed in the normal of said switch position and from said source to said sec- 'ond terminal of said loop closed in the three other positions of said switch means, Ia circuit for said second relay from said source to said rst loop terminal separately closed only in said three other positions of said switch means, whereby said second relay is-connected with the loop 4 for eifecting signal control only in said three other positions but not in the normal position of said switch means, said first relay being operatively connected with'said loop for signal contact in the normal and three other positionsv of 4 said switch means, front contacts for said relays' connected together and back contacts for said relays connected together, relay armature contacts controlled by said iirst and second relays, a call register, and circuit kconnections including 5 said contacts 'and armatures controlled by said switch means for controlling said register, by said rst relay only, in the normal position of said switch means, and independently by` either` of said relays in said three other positions of said ,3 switch means. GILBERT S. VERNAM. RONALD S. WISHART. 

